The present invention is directed to the field of shaft position sensors which are to operate on multiturn shafts. It is technically feasible to provide an unambiguous signal from a shaft encoding device to detect the position of a single turn of the shaft. However, such is not the case with a shaft that can operate through a multiplicity of turns.
Often it is desired to provide such an output with regard to a multiturn shaft. Such is the case with detecting the position of the steering wheel of a motor vehicle. Typically a steering wheel can be operated for multiple turns from full left turn to full right turn. Merely detecting the position of the shaft with an ambiguity of a full turn would not unambiguously detect the position of the controlled wheels. Thus, such a system without more would be inadequate to provide an indication of the turning of the vehicle.
This problem can be solved with auxiliary equipment as a part of the sensor device. A mechanical reduction gear could be employed to reduce the multiturn movement into movement of less than a single turn of a secondary shaft. A shaft encoder on this secondary shaft could thus resolve the ambiguity. Alternatively, a shaft encoder on the primary shaft could be connected to an electronic system to keep count of the turns both clockwise and counter clockwise to provide resolution of the ambiguity. Because of drawbacks in these systems, such as mechanical backlash in the case of a mechanical reduction system and the necessity for additional complex circuits for electronic systems, there is a need in the art for a simple system to unambiguously detect the position of a multiturn shaft.
A further problem arises in typical mechanically coupled sensors. Devices, built to less than perfect tolerances will exhibit backlash which tends to degrade performance, accuracy and repeatability of the sensor device. System wear over time tends to further degrade performance by increasing backlash.